Electric power converter apparatus which attenuates frequency components of ripple in output current

ABSTRACT

An electric power converter apparatus incorporates a plurality of electric power converter circuits having respective output terminals connected in common, with output power being produced from the common output terminals. Each converter circuit uses an identical switching frequency, in executing power conversion based on PWM control of switching by a plurality of switching elements. The switching operations of the respective converter circuits mutually differ in phase, by an amount determined in accordance with the currently applied PWM duty ratio. The phase difference value is predetermined for minimizing the amplitude of specific harmonic frequency components of a ripple current component in the output current from the apparatus.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and incorporates herein by referenceJapanese Patent First Application No. 2014-125545 filed on Jun. 18,2014.

BACKGROUND OF THE INVENTION

1. Field of Application

The present invention relates to an electric power converter apparatusincorporating switching elements, which performs electric powerconversion by switching operation of the switching elements.

2. Description of Related Art

Types of electric power converter apparatus are known, such as anelectric power source apparatus disclosed in Japanese patent publicationNo. 2009-100515 (designated in the following as reference 1), in whichswitching elements of a plurality of electric power converter circuitsare switched to perform electric power conversion, under control ofrespective control circuits, with respective output currents from theelectric power converter circuits being combined to constitute theoutput current from the apparatus.

The electric power source apparatus of reference 1 incorporates threeDC-DC converters and three controllers (control circuits). Each DC-DCconverter incorporates switching elements, and executes switching of theswitching elements to perform conversion of electric power that issupplied to input terminals, and supplies converted electric power fromoutput terminals. Each controller generates a PWM (pulse widthmodulation) signal for controlling the switching elements of acorresponding one of the DC-DC converters. The phases of the PWM signalsfrom the three DC-DC converters are evenly dispersed, thereby evenlydispersing the phase of a ripple current (produced as a result of theswitching of the switching elements) in the output current from theelectric power source apparatus. The objective of this is to reduce theamplitude of the ripple current.

However with that method, although the amplitude of the ripple currentcan be reduced, there is no reduction in amplitude of ripple currentfrequency components, i.e., components at frequencies which areharmonics of the ripple current frequency. As a result, substantialelectrical noise may be produced by the output current from such anelectric power converter apparatus, at frequencies which aresufficiently high to cause interference with radio reception.

SUMMARY OF THE INVENTION

Hence it is desired to overcome the above problem, by enabling areduction of the amplitude of specific ripple current frequencycomponents contained in the output current from an electric powerconverter apparatus which executes electric power converter by switchingof switching elements.

To achieve this, the invention provides an electric power converterapparatus having a plurality of electric power converter circuitsconnected to control circuitry. Respective output terminals of theelectric power converter circuits are connected in common, i.e., with anoutput current from the apparatus being a combination of respectiveoutput currents from the electric power converter circuits. Each of theelectric power converter circuits incorporates a plurality of switchingelements, and is controlled by a corresponding PWM (pulse widthmodulation) control signal supplied from the control circuitry, forexecuting switching of the switching elements, to thereby convert inputelectric power (supplied to the input terminals) to output electricpower that is supplied from the output terminals.

Specifically, the control circuitry generates a plurality of PWM signalsof identical frequency, mutually differing in phase by a set value ofphase difference, and supplies each PWM signal to a corresponding one ofthe electric power converter circuits, for controlling switching of thecorresponding switching elements. The set value of phase difference isdetermined such as to minimize the amplitude of specific ripple currentfrequency components contained in the output current from the electricpower converter apparatus, i.e., frequency components that are within aspecific frequency range.

According to embodiments described in the following, each of theplurality of PWM signals is modulated by an identical set value of dutyratio, and the control circuit includes a data map and a phasedifference setting section. The data map consists of stored data whichrelate each of respective values of the PWM duty ratio to acorresponding value of phase difference. Each value of phase differenceis predetermined such that when it is selected (to be the set value ofphase difference), and the corresponding duty ratio is the set value ofduty ratio, the amplitude of the specific ripple current frequencycomponents is minimized. To achieve this, the phase difference settingsection obtains (from the data map) the phase difference valuecorresponding to the PWM duty ratio that is currently set. That value ofphase difference is then set as the specific phase difference betweenthe plurality of PWM signals.

In that way as the duty ratio of the plurality of PWM signals becomeschanged, the phase difference between them becomes changed accordingly,such as to minimize the amplitude of the ripple current frequencycomponents. High-frequency electrical noise resulting from these ripplecurrent frequency components in the output current from the electricpower converter apparatus, in particular, electrical noise which maycause interference with reception by a radio receiver, can thereby beeffectively reduced.

The set value of duty ratio may be determined, for example, inaccordance with a command value of output voltage from the electricpower converter apparatus.

The data to be stored as the contents of the data map (i.e., phasedifference values corresponding to respective values of duty ratio) maybe advantageously derived based on results from computer simulation,rather than by executing extensive testing and measurement operations toobtain the required information. In that way the necessary contents ofthe data map can be readily established.

From another aspect, the control section may comprise a plurality ofdata maps (corresponding to respectively different specific frequencyranges) each of the form described above. In that case, the controlsection further includes a frequency component analyzer section (whoseanalysis results express the respective amplitudes of the ripple currentfrequency components within each of the specific frequency ranges) and afrequency component designation section. The phase difference valuesheld in each data map are predetermined for minimizing the amplitude ofthe ripple current frequency components that are within the frequencyrange that corresponds to that particular data map. The frequencycomponent designation section serves to specify a high-amplitude one ofthe ripple current frequency components as being a designated frequencycomponent. The data map whose corresponding frequency range contains thefrequency of the designated frequency component is selected for use,i.e., for setting a PWM phase difference value that corresponds to thecurrently set value of duty ratio.

Preferably, a target value of frequency component amplitude ispredetermined and stored in a memory device. When the amplitude of anyof the ripple current frequency components within any of the specificfrequency ranges is judged (based on the frequency analysis results) toexceed the target value, the frequency component whose amplitude exceedsthe target value by the greatest amount is specified as being thedesignated frequency component, and the data map corresponding to thefrequency range containing the designated frequency component is thenselected for use.

In that way, the amplitude of the ripple current frequency componentscan be achieved effectively, by selecting the most appropriate data mapin accordance with the respective frequencies and amplitudes of theripple current frequency components that are presently contained in theoutput current from the electric power converter apparatus.

The control circuit may include both a frequency component analyzersection and also a data map correction section. The data map correctionsection serves to correct the respective phase difference values held ina data map, based on the analysis results from the frequency componentanalyzer section. For example, when a duty ratio has become set for thePWM signals, processing may be executed by the data map correctionsection for replacing the corresponding phase difference value (thevalue currently held in the data map) by a corrected phase differencevalue, which will more effectively reduce the amplitude of the ripplecurrent frequency components.

The invention is particularly applicable to an electric power converterapparatus for installation in a motor vehicle, since the inventionenables a reduction of interference with reception by a radio receiverof the vehicle, when the interference is caused by electrical noiseproduced by operation of the electric power converter apparatus.

In the following description of embodiments and in the appended claims,“minimizing an amplitude of ripple current frequency components” is tobe understood as reducing the amplitude of the ripple current frequencycomponents as far as possible under the condition in which an electricpower converter apparatus is currently operating.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of a first embodiment of an electric powerconverter apparatus;

FIG. 2 is a block diagram of a phase difference setting circuit shown inFIG. 1;

FIG. 3 is a graph showing the relationship of a phase difference betweentwo PWM signals to the amplitudes of ripple current frequency componentscontained in the output current from the converter apparatus of FIG. 1,when the duty ratio of the PWM signals is 40%;

FIG. 4 is a graph showing the relationship between the phase differenceof the PWM signals and the maximum amplitude of the ripple currentfrequency components, when the duty ratio of the PWM signals is 40%;

FIG. 5 is a graph showing the relationship between the phase differenceof the PWM signals and the maximum amplitude of the ripple currentfrequency components, when the duty ratio of the PWM signals is 30%;

FIG. 6 is a graph showing the relationship between the phase differenceof the PWM signals and the maximum amplitude of the ripple currentfrequency components, when the duty ratio of the PWM signals is 35%;

FIG. 7 is a graph showing the relationship between the phase differenceof the PWM signals and the maximum amplitude of the ripple currentfrequency components, when the duty ratio of the PWM signals is 45%;

FIG. 8 is a graph showing the relationship between the phase differenceof the PWM signals and the maximum amplitude of the ripple currentfrequency components, when the duty ratio of the PWM signals is 50%;

FIG. 9 is a circuit diagram of a second embodiment of an electric powerconverter apparatus;

FIG. 10 is a block diagram of a phase difference setting circuit shownin FIG. 9;

FIG. 11 is a circuit diagram of a third embodiment of an electric powerconverter apparatus;

FIG. 12 is a block diagram of a phase difference setting circuit shownin FIG. 11; and,

FIG. 13 is a block diagram of a phase difference setting circuit of analternative form of the third embodiment.

DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of an electric power converter apparatus are described inthe following, each being a DC-to-DC converter for installation in amotor vehicle, for converting DC power supplied from a high-voltagebattery to DC power at a controlled voltage, which is supplied to anelectrical load of the vehicle.

First Embodiment

A first embodiment will be described referring to FIG. 1. As shown, anelectric power converter apparatus 1 of this embodiment receives DCpower from a high-voltage battery B1 of a vehicle, and converts this tooutput DC power which is supplied to an electrical load S1 of thevehicle. The electric power converter apparatus 1 includes two electricpower converter circuits 10 and 11, voltage sensors 12 and 13, and twocontrol circuits 13 and 14.

The electric power converter circuit 10 converts the input DC power,supplied from the high-voltage battery B1, to output DC power that issupplied to the electrical load S1, at a different voltage from that ofthe input DC power, with the output DC power electrically insulated fromthe input DC power. As shown, the electric power converter circuit 10includes a switching circuit 100, a transformer 101, a rectifier circuit102 and a drive circuit 103.

The switching circuit 100 converts the DC power from the high-voltagebattery B1 to AC power by switching operation of a set of FETs 100 a to100 d, functioning as respective switching elements.

The FETs 100 a, 100 b are connected in series, as are the FETs 100 c,100 d, with the source electrodes of the FETs 100 a, 100 c respectivelyconnected to the drain electrodes of the FETs 100 b, 100 d. The drainelectrodes of the FETs 100 a, 100 b are connected in common to an inputterminal I100 of the electric power converter circuit 10 (and therebyconnected to the positive terminal of the high-voltage battery B1),while the source electrodes of the FETs 100 a, 100 b are connected incommon to an input terminal I101 of the electric is power convertercircuit 10 (and thereby connected the negative terminal of thehigh-voltage battery B1). The junction point of the FETs 100 a, 100 band the junction point of the FETs 100 c, 100 d are connected toopposite ends of a primary winding 101 a of a transformer 101. The gateelectrodes of the FETs 100 a, 100 b, 100 c, 100 d are respectivelyconnected to receive drive signals (switching control signals) from adrive circuit 103.

The transformer 101 converts AC power supplied to its primary winding101 a to AC power at a different voltage, produced from secondarywindings 101 b, 101 c of the transformer 101, which are connected to arectifier circuit 102.

The rectifier circuit 102 includes diodes 102 a, 102 b, an inductor 102c, and a capacitor 102 d, and rectifies the AC power supplied from thesecondary windings 101 b, 101 c to obtain DC power that is supplied tothe electrical load S1. The diodes 102 a, 102 b rectify the AC powersupplied from the secondary windings 101 b, 101 c, with the anodes ofthe diodes 102 a and 102 b being respectively connected to opposite endsof the secondary windings 101 b, 101 c, and the cathodes of the 102 aand 102 a being connected in common to one end of the inductor 102 c.The junction point of the secondary windings 101 b, 101 c is connectedto one side of the capacitor 102 d and to the terminal O101 (thenegative output terminal of the electric power converter circuit 10)while the other side of the capacitor 102 d is connected to the otherend of the inductor 102 c and to the terminal O100 (the positive outputterminal of the electric power converter circuit 10). The electricalload S1 is connected between the output terminals O100 and O101.

The drive circuit 103 receives a PWM signal (described hereinafter) froma control circuit 14, and drives the FETs 100 a, 100 b, 100 c, 100 dbased on that PWM signal. Specifically, drive signals (switching controlsignals) outputted from the drive circuit 103 are respectively appliedto the gate electrodes of the FETs 100 a, 100 b, 100 c, 100 d.

The electric power converter circuit 11 converts the input DC power,supplied from the high-voltage battery B1, to output DC power that issupplied to the electrical load S1, at a different voltage from that ofthe input DC power, with the output DC power being electricallyinsulated from the input DC power. As shown, the electric powerconverter circuit 11 includes a switching circuit 110, a rectifiercircuit 112, and a drive circuit 113, which have respectively identicalcircuit configurations to those of the switching circuit 100, therectifier circuit 102 and the drive circuit 103 of the electric powerconverter circuit 10. Input terminals I110 and I111 of the electricpower converter circuit 11 are respectively connected to the inputterminal I100 and I101 of the electric power converter circuit 10, andhence to the high-voltage battery B1. Output terminals O110 and O111 ofthe electric power converter circuit 11 are respectively connected tothe output terminals O100 and O101 of the electric power convertercircuit 10, and hence are connected across the electrical load S1.

A voltage sensor 12 is connected between the input terminals I100, I101of the electric power converter circuit 10 and between the inputterminals I110, I111 of the electric power converter circuit 11, todetect the input voltage of the electric power converter circuit 10 andelectric power converter circuit 11, and inputs the detection results tothe control circuit 14 and the control circuit 15. A voltage sensor 13is connected between the output terminals O100, O101 of the electricpower converter circuit 10 and between the output terminals O110, O111of the electric power converter circuit 11, to detect the output voltageof the electric power converter circuit 10 and electric power convertercircuit 11, and inputs the detection results to the control circuit 14and the control circuit 15.

The control circuit 14 controls the electric power converter circuit 10based on an (externally supplied) output voltage command signal whichexpresses a required value of output DC voltage from the electric powerconverter apparatus 1, and on detected values of input voltage andoutput voltage of the electric power converter circuits 10 and 11 fromthe voltage sensors 12 and 13. The control circuit 14 generates the PWMsignal which controls the switching of the FETs 100 a-100 d. With thisembodiment, the frequency of the PWM signal from the control circuit 14is used as a reference PWM signal frequency for controlling the electricpower converter circuit 11. As shown, the control circuit 14 includes anoscillator circuit 140, a reference signal generating circuit 141, a PWMcontrol value setting circuit 142 and a PWM signal generating circuit143.

The oscillator circuit 140 generates a pulse signal at the PWM signalreference frequency (with this embodiment, 100 kHz), which is suppliedto the reference signal generating circuit 141 and the PWM signalgenerating circuit 143. The term “pulse signal” is used herein tosignify a signal consisting of a series of fixed-duration pulses.

The reference signal generating circuit 141 produces a reference signalwhich is synchronized with the pulse signal from the oscillator circuit140, and which is inputted to the control circuit 15.

The PWM control value setting circuit 142 sets a control value of dutyratio for the PWM signal switching operation of the switching circuit100, and outputs the control value to the PWM signal generating circuit143. The PWM signal generating circuit 143 thereby generates a PWMsignal at 100 kHz, modulated by the control value of duty ratio. Thecontrol value of PWM duty ratio is determined based on the externallysupplied voltage command signal and on the voltage values detected bythe voltage sensors 12 and 13. With this embodiment, the referencesignal from the reference signal generating circuit 141 is identical infrequency to the PWM signal.

The PWM signal generating circuit 143 thus generates the PWM signalbased on the pulse signal received from the oscillator circuit 140 andon the control value of duty ratio received from the PWM control valuesetting circuit 142. Specifically, the PWM signal has the frequency (100kHz) of the pulse signal from the oscillator circuit 140.

The control circuit 15 produces a PWM signal for controlling switchingof FETs (not shown in the drawings) in the switching circuit 110 of theelectric power converter circuit 11, with the PWM signal being generatedbased upon the output voltage command signal, the detected voltagevalues from the voltage sensors 11 and 13, and the reference signalsupplied from the reference signal generating circuit 141 of the controlcircuit 14. The control circuit 15 incorporates an oscillator circuit150, a PWM control value setting circuit 151, a phase difference settingcircuit 152 and a PWM signal generating circuit 153.

The oscillator circuit 150 generates a pulse signal which is controlledto maintain the same frequency as the pulse signal generated by theoscillator circuit 140 of the control circuit 14, but which is notsynchronized with (i.e., is not locked to the same phase as) the signalfrom the oscillator circuit 140. The pulse signal from the oscillatorcircuit 150 is inputted to the phase difference setting circuit 152.

The PWM control value setting circuit 151 sets a control value of PWMduty ratio, which in principle is identical to the value of duty ratiothat is set by the PWM control value setting circuit 142 as describedabove, i.e., being determined similarly based on the output voltagecommand signal and on the voltage detection results from the voltagesensors 12 and 13. That control value is inputted to the PWM signalgenerating circuit 153 from the PWM control value setting circuit 151,for determining the duty ratio of a PWM signal that is generated by thePWM signal generating circuit 153 and supplied to the drive circuit 113of the electric power converter circuit 11.

The phase difference setting circuit 152 determines a phase differencevalue which is a required phase difference between the PWM signalsrespectively produced from the control circuits 14 and 15. Specifically,the phase difference setting circuit 152 inputs a pulse signal to thePWM signal generating circuit 153 which is identical in frequency to thepulse signal generated by the oscillator circuit 140 (i.e., with thisembodiment, nominally 100 kHz) and which differs in phase from the pulsesignal generated by the oscillator circuit 140 by the required phasedifference. The required PWM phase difference is determined based uponthe reference signal which is inputted from the reference signalgenerating circuit 141 of the control circuit 14, the pulse signal whichis inputted from the oscillator circuit 150, and on the duty ratio valuethat is currently set by the PWM control value setting circuit 151.

The configuration of the phase difference setting circuit 152 is shownin the block diagram of FIG. 2. As shown, the phase difference settingcircuit 152 incorporates a data map storage section 152 a and a phasedifference setting section 152 b. A data map held in the data mapstorage section 152 a consists of stored data which express, for each ofa plurality of PWM duty ratio values, a corresponding value of phasedifference. The corresponding phase difference value is the phasedifference that is required to be set (between the PWM signals from thecontrol circuits 14 and 15 respectively) when the corresponding dutyratio value is set.

Each of the phase difference values in the data map is predeterminedsuch that as to minimize the amplitude of specific ripple currentfrequency components (described in the following) when the switchingcircuits 100 and 110 execute switching operation using the duty ratiocorresponding to that phase difference value.

As described above, the PWM signal generating circuit 143 generates a100 kHz PWM signal for switching the FETs 100 a-100 d of the switchingcircuit 100 at 100 kHz, while the PWM signal generating circuit 153generates a 100 kHz PWM signal differing in phase from the output signalof the PWM signal generating circuit 143 by a specific amount, i.e., bythe phase difference value that is currently set by the phase differencesetting circuit 152. Hence the FETs of the switching circuit 110 areswitched at 100 kHz, with the set value of phase difference between theswitching timings of these FETs and those of the switching circuit 100.Since the switching frequency is 100 kHz and full-wave rectification isapplied in the rectifier circuit 102, the output current from theelectric power converter apparatus 1 (combination of respective outputcurrents from the electric power converter circuit 10 and the electricpower converter circuit 11) contains a 200 kHz ripple current componentand also high-frequency components (referred to in the following asripple current frequency components) having frequencies that arerespective harmonics of 200 kHz

The phase difference values in the data map of the data map storagesection 152 a are predetermined for minimizing the amplitude of ripplecurrent frequency components that are within an AM-band radio frequencyrange. The AM-band frequency range of a radio receiver installed in avehicle is typically 500 kHz˜1.7 MHz. Hence, the 3^(rd)-order to8^(th)-order harmonics of 200 kHz (600 kHz, 800 kHz, 1 MHz, 1.2 MHz, 1.4MHz, 1.6 MHz) are each within that AM-band frequency range.

FIG. 3 shows graphs of the results of computer simulation (for the caseof a PWM duty ratio of 40% being specified by the PWM control valuesetting circuit 151) which relate the phase difference between the 100kHz signals produced from the control circuits 14 and 15 and respectiveamplitudes of high-frequency components of the ripple current,specifically the 3^(rd)-order to 8^(th)-order harmonics of 200 kHz. Theresults are shown for values of phase difference within the range0°˜180°.

The term “amplitude of the ripple current frequency components” is usedherein to refer to the amplitude of the highest-amplitude one of aplurality of ripple current frequency components.

FIG. 4, corresponding to FIG. 3, shows the relationship between thephase difference values and the amplitude of the ripple currentfrequency components (as defined above), when the PWM duty ratio is 40%.As illustrated, the minimum amplitude is reached when the phasedifference is 156°.

Similarly as shown in FIG. 5, when the PWM duty ratio is 30%, theamplitude of the ripple current frequency components reaches a lowestvalue when the phase difference is 162°. As shown in FIG. 6, when thePWM duty ratio is 35%, the lowest value of the amplitude of the ripplecurrent frequency components occurs when the phase difference is 126°.As shown in FIG. 7, when the PWM duty ratio is 45%, the lowest value ofthe amplitude of the ripple current frequency components occurs when thephase difference is 167°. As shown in FIG. 8, when the PWM duty ratio is50%, the lowest value of the amplitude of the ripple current frequencycomponents occurs when the phase difference is 180°.

The data map held in the data map storage section 152 a expresses theabove information, obtained from computer simulation results. That is,the map data express (for each of respective PWM duty ratios 30%, 35%,45%, 50%, etc.,) the value of phase difference that is required to beset between the PWM signals produced from the control circuits 14 and15, for minimizing the amplitude of the ripple current frequencycomponents that have frequencies within the AM-band frequency range,when the corresponding duty ratio is applied.

The phase difference setting section 152 b is a circuit block whichaccesses the map data held in the data map storage section 152 a andalso receives, from the PWM control value setting circuit 151, the valueof duty ratio that is currently required to be set, receives thereference signal from the reference signal generating circuit 141, andreceives the 100 kHz pulse signal produced from the oscillator circuit150. Based on these, the phase difference setting section 152 bgenerates a pulse signal which differs in phase from the output signalfrom the oscillator circuit 140 of the control circuit 14 by the setvalue of phase difference and is of identical frequency to the outputsignal from the oscillator circuit 140, and which is inputted to the PWMsignal generating circuit 153. The phase difference which is set by thephase difference setting section 152 b is the value, held in the mapdata of the data map storage section 152 a, which corresponds to thevalue of duty ratio that is currently set by the PWM control valuesetting circuit 151.

Based on the currently set value of duty ratio, and on the pulse signalreceived from the phase difference setting circuit 152, the PWM signalgenerating circuit 153 generates the PWM signal which controls switchingoperation of the switching circuit 110 of the electric power convertercircuit 11. The PWM signal is outputted from the PWM signal generatingcircuit 153 to the drive circuit 113 of the electric power convertercircuit 11. In principle, the PWM signal generated by the PWM signalgenerating circuit 153 has an identical duty ratio to that generated bythe PWM signal generating circuit 143.

The operation of the first embodiment will be described referring toFIGS. 1 and 2. When operation of the electric power converter apparatus1 has started, the oscillator circuit 140 commences generating the 100kHz pulse signal used as a reference for PWM signal generation, withthat pulse signal being outputted to the reference signal generatingcircuit 141 and the PWM signal generating circuit 143. The referencesignal generating circuit 141 generates a reference signal which issynchronized with the pulse signal from the oscillator circuit 140, andwhich is supplied to the phase difference setting circuit 152 of thecontrol circuit 15.

The PWM control value setting circuit 142 sets a required value of PWMduty ratio, based upon the externally supplied voltage command signal,and upon values of input (battery) voltage and output supply voltage ofthe electric power converter circuit 10, respectively detected by thevoltage sensor 12 and the voltage sensor 13, and inputs that duty ratiovalue to the PWM signal generating circuit 143. Based on the pulsesignal from the oscillator circuit 140 and the duty ratio value that isset by the PWM control value setting circuit 142, the PWM signalgenerating circuit 143 generates the 100 kHz PWM signal which isoutputted to the drive circuit 103 of the electric power convertercircuit 10.

The drive circuit 103 drives the FETs 100 a-100 d in accordance with thePWM signal received from the PWM signal generating circuit 143, with theFETs 100 a-100 d thereby executing synchronized switching at 100 kHz.Specifically, the FETs 100 a and 100 c execute complementary switchingwith the FETs 100 b and 100 d respectively. The DC power from thehigh-voltage battery B1 is thereby converted to AC power which issupplied to the primary winding 101 a of the transformer 101. AC powerat a different voltage is outputted from the secondary windings 101 b,101 c of the transformer 101, electrically isolated from the primaryside power. The output AC power from the transformer 101 is rectified toDC power by the diodes 102 a, 102 b, which is smoothed by the inductor102 c and capacitor 102 d, and supplied to the electrical load S1.

The PWM control value setting circuit 151 sets a duty ratio value in thesame manner (and based on the same input signals) as described for thePWM control value setting circuit 142, i.e., sets the same duty ratiovalue as the PWM control value setting circuit 142, in principle. Theset value of duty ratio is supplied from the PWM control value settingcircuit 151 to the phase difference setting circuit 152 and the PWMsignal generating circuit 153.

The phase difference setting section 152 b of the phase differencesetting circuit 152 obtains a required value of phase difference, fromthe data map of the data map storage section 152 a, corresponding to theduty ratio value that is currently set by the PWM control value settingcircuit 151. Based on that phase difference value, the reference signalfrom the reference signal generating circuit 141, the pulse signal fromthe oscillator circuit 150 and the control value of duty ratio receivedfrom the PWM control value setting circuit 151, the phase differencesetting section 152 b generates a pulse signal which differs in phasefrom the PWM signal generated by the PWM signal generating circuit 143by the set value of phase difference and which is of identical frequencyto the PWM signal from the PWM signal generating circuit 143. The pulsesignal generated by the phase difference setting section 152 b isinputted to the PWM signal generating circuit 153.

As described above referring to FIGS. 3 and 4, the value of phasedifference that is obtained by the phase difference setting circuit 152from the data map of the data map storage section 152 a is a valuewhereby the amplitude of high-frequency ripple components in the outputcurrent supplied from the electric power converter apparatus 1 (atfrequencies within the AM-band radio reception range) is minimized.

In the same way as for the FETs of the switching circuit 100, the FETsof the switching circuit 110 execute switching that is controlled bydrive signals from the drive circuit 113, synchronized with the 100 kHzPWM signal from the PWM signal generating circuit 153 that is inputtedto the drive circuit 113. The electric power converter circuit 11thereby converts the DC power supplied from the high-voltage battery B1to AC power that is supplied to the electrical load S1, in the samemanner as described for the electric power converter circuit 10, i.e.,with the transformer 111 and the rectifier circuit 112 of the electricpower converter circuit 11 functioning as described hereinabove for thetransformer 101 and the rectifier circuit 102 of the electric powerconverter circuit 10 respectively.

In principle the electric power converter circuits 10 and 11respectively produce the same value of output voltage, which is appliedto the electrical load S1 as the output voltage from the output voltagefrom the electric power converter apparatus 1. The combination ofrespective output currents from the electric power converter circuit 10and the electric power converter circuit 11 constitute the outputcurrent of the electric power converter apparatus 1, supplied to theelectrical load S1. The DC power from the electrical load S1 is therebyconverted by the electric power converter apparatus 1 to output DC powerat a voltage determined by the output voltage command signal, with theoutput power being electrically insulated from the input power.

The effects obtained with the first embodiment are as follows.

The electric power converter apparatus 1 incorporates two electric powerconverter circuits 10 and 11, and two control circuits 14 and 15. Theelectric power converter circuits 10 and 11 each incorporate FETs asswitching elements, and execute switching in accordance with PWM signalsproduced by the control circuits 14 and 15 respectively. An input DCvoltage, applied to the pairs of input terminals I100, I101 and I100,I101 of the electric power converter circuit 10 and electric powerconverter circuit 11 respectively, is converted to an output DC voltagewhich appears on the pairs of output terminals O100, O101 and O110, O111of the electric power converter circuit 10 and electric power convertercircuit 11 respectively.

With such an electric power converter apparatus utilizing a plurality ofelectric power converter circuits in combination, it is possible todisperse the respective phases of the PWM signals which controlswitching in the various electric power converter circuits, as describedin reference document 1 above. That method enables a decrease in theamplitude of a ripple current in the output current from the apparatus,having a frequency determined by the switching frequency of the electricpower converter circuits, i.e., 200 kHz in the case of the aboveembodiment. However the amplitude of high-frequency components in theoutput current from the apparatus, at harmonic frequencies of the ripplecurrent, is not reduced. Hence such a phase dispersion technique cannotreduce the level of electrical noise produced by the electric powerconverter apparatus, at frequencies which are sufficiently high as tocause interference in AM radio reception.

However with the first embodiment described above, a phase differencebetween the PWM signals which control switching in the electric powerconverter circuits 10 and 11 respectively is controlled such as toeffectively reduce the amplitude of specific frequency components of theripple current in the output current from the electric power converterapparatus 1. This is achieved by appropriately determining the phasedifference in accordance with the duty ratio that is currently set forthe PWM signals. The electrical noise resulting from these frequencycomponents can thereby be reduced.

With the first embodiment, the control circuit 15 includes the phasedifference setting circuit 152 and the PWM signal generating circuit153, with the phase difference setting circuit 152 being formed of thedata map storage section 152 a and phase difference setting section 152b. The data map storage section 152 a stores memory map data whichrelates values of PWM signal duty ratio to corresponding values of phasedifference. As described above, the phase difference between therespective PWM signals produced from the PWM signal generating circuit143 and PWM signal generating circuit 153 is set by the phase differencesetting circuit 152, using the stored memory map data, at a value inaccordance with the PWM duty ratio that is currently being applied. Thephase relationship between the PWM signals produced from the PWM signalgenerating circuit 143 and PWM signal generating circuit 153 can therebybe reliably determined such as to appropriately reduce the amplitude ofthe ripple current frequency components which are within a specific AMradio reception band.

With the first embodiment, the memory map data are derived with respectto a specific AM radio reception band by employing computer simulation.This enables the map data to be more readily generated than if thememory map data were to be based on results from actual measurements.

With the first embodiment, when the electric power converter apparatuses10 and 11 and the control circuits 14 and 15 are installed in a motorvehicle, i.e., when the electric power converter apparatus 1 is used ina vehicle in which an AM radio receiver is installed, interference dueto electrical noise in the AM frequency band can be effectively reduced.

With the above embodiment, the PWM signal frequency is 100 kHz, howeverthe invention is not limited to any specific frequency.

The first embodiment utilizes two electric power converter apparatuses10 and 11 and two corresponding control circuits 14 and 15. However itwould be equally possible for the electric power converter apparatus tobe formed of is three or more electric power converter circuits. It isonly necessary to establish an appropriate phase differences between therespective PWM signals which control the electric power convertercircuits, in accordance with a PWM duty ratio that is currently set(i.e. a duty ratio that is to be applied by each of the electric powerconverter circuits), such as to minimize the amplitude of specifichigh-frequency components in the output current from the apparatus. Inthe above description, the circuits 14 and 15 are described asrespective control circuits. However these are not mutually independentcircuits. They can be considered to constitute a single control circuit,requiring only a single PWM control value setting circuit. That is, sucha single control circuit determines a phase difference value based on aPWM control value, and thereby produces a plurality of control signals(PWM signals) having respectively identical frequency, identical dutyratio, and mutually different phase.

Hence it will be understood that the invention is not limited to theconfiguration shown in FIG. 1 for producing the PWM signals that aresupplied to control the plurality of electric power converter circuits.

It will further be understood that overall control of the phasedifference setting circuit 152 for performing the functions describedabove can readily be implemented by a usual type of microcomputer,operating in accordance with a stored program. In particular it will beapparent that the functions described for the phase difference settingsection 152 b can readily be implemented under such control, inconjunction with a phase locked loop (PLL) circuit, and a circuit fordelaying the reference signal by a controlled amount (an equal to therequired phase difference). In that case, the PLL is configured to besynchronized with the delayed reference signal, and to provide the 100kHz pulse signal that is supplied to the PWM signal generating circuit153.

Second Embodiment

A second embodiment of an electric power converter apparatus isdescribed in the following. This embodiment utilizes a data map as forthe first embodiment, but differs from the first embodiment in that thephase difference values stored in the data map can be corrected duringoperation of the apparatus, as described in the following.

The electric power converter apparatus 2 of the second embodiment willbe described referring to FIGS. 9 and 10. As shown in FIG. 9, theoverall configuration is similar to the electric power converterapparatus 1 of the first embodiment, with DC power from a high-voltagebattery B2 of a vehicle being converted to an DC power at a differentvoltage, and supplied to an electrical load S2 of the vehicle.

Electric power converter circuits 20 and 21 of this embodiment areidentical to the circuits 10 and 11 respectively of the firstembodiment. The voltage sensors 22 and 23 of the second embodiment areof identical type to the sensors 12 and 13 of the first embodiment, andthe switching circuits 200 and 210, transformers 201, 211, drivecircuits 203, 213 are respectively identical to the switching circuits100 and 110, transformers 101, 111, and drive circuits 103, 113 of thefirst embodiment

Essentially, the second embodiment differs from the first embodiment byfurther incorporating a current sensor 26, and with respect to theconfiguration and operation of a control circuit 25.

The current sensor 26 is connected between the electrical load S2 and anoutput terminal O200 of the electric power converter circuit 20, anddetects the output current supplied from the electric power converterapparatus 2 to the electrical load S1 (i.e., combined output currentsfrom the electric power converter circuits 10 and 11). A signalexpressing the detection results is supplied to the control circuit 25from the current sensor 26.

An oscillator circuit 250, PWM control value setting circuit 251 and PWMsignal generating circuit 253 of the control circuit 25 are respectivelyidentical to the oscillator circuit 150, the PWM control value settingcircuit 151 and the PWM signal generating circuit 153 in the controlcircuit 15 of the first embodiment. Other than with respect to theoperation of a phase difference setting circuit 252, described in thefollowing, the functioning of the control circuit 25 is identical tothat of the control circuit 15 of the first embodiment. That is, thephase difference setting circuit 252 produces a pulse signal whichdiffers in phase from the output signal of the oscillator circuit 140 bya specific amount, and which is supplied to the PWM signal generatingcircuit 253. The PWM signal generating circuit 253 generates a PWMsignal whose phase and frequency are determined by the pulse signalsupplied from the phase difference setting circuit 252, and having aduty ratio that is set by the PWM control value setting circuit 251.

As shown in FIG. 10, the phase difference setting circuit 252 is formedof a data map storage section 252 a, a phase difference setting section252 b, a frequency component analyzer section 252 c, and a data mapcorrection section 252 d. The data map storage section 252 a isidentical to the data map storage section 152 a of the first embodiment.However in the case of the phase difference setting circuit 252, thecontents of the data map storage section 252 a can be corrected(compensated) if necessary, after the electric power converter apparatus2 has been set in operation. A rewritable type of non-volatile memorydevice is used to constitute the data map storage section 252 a, so thateach currently stored phase difference value can be replaced by acorrected value.

The phase difference setting section 252 b has a similar function tothat of the phase difference setting section 152 b of the firstembodiment. However in addition, the phase difference setting section252 b supplies the currently set values of PWM signal duty ratio (fromthe PWM control value setting circuit 251) and PWM signal phasedifference (from the data map storage section 252 a) to the data mapcorrection section 252 d.

The frequency component analyzer section 252 c receives the detectionresults for the output current from the electric power converterapparatus 2, from the current sensor 26, and analyses the frequencycomponents of the ripple current in that output current. The analysisresults from the frequency component analyzer section 252 c express themaximum frequency component amplitude (defined above in the descriptionof the first embodiment) within the AM radio reception range (500kHz˜1.7 MHz). The currently obtained analysis result (maximum frequencycomponent amplitude) is supplied to the data map correction section 252d.

The data map correction section 252 d receives signals from the phasedifference setting section 252 b expressing the values of PWM signalduty ratio and phase difference that are currently set, and alsoreceives the analysis result (i.e., maximum frequency componentamplitude value) that is currently obtained by the frequency componentanalyzer section 252 c.

The operation of the electric power converter apparatus 2 of the secondembodiment will be described referring to FIGS. 9 and 10. Other thanwith respect to a map data correction function, the operation of thephase difference setting section and the data map of this embodiment isidentical to that of the first embodiment, so that further descriptionis omitted.

Based on the values of PWM signal duty ratio and PWM signal phasedifference supplied from the phase difference setting section 252 b andon the analysis result obtained by the frequency component analyzersection 252 c, the data map correction section 252 d corrects (i.e.,updates to an amended value) the corresponding phase difference valuethat is stored in the data map storage section 252 a.

A data map correction operation can be executed as follows. The data mapcorrection section successively varies the set value of phase difference(e.g., within the range 0° to 90° shown in FIG. 4), and detects theoptimum phase difference (at which the amplitude of the ripple currentfrequency components becomes a minimum) based on the output values fromthe frequency component analyzer section 252 c. If the optimum phasedifference is found to differ from the phase difference value that isheld in the data map storage section 252 a in correspondence with thecurrently set value of duty ratio, then the stored value of phasedifference is corrected to the optimum value.

The advantages of the above-described data map correction function ofthe second embodiment, executed by the data map correction section 252 din conjunction with the frequency component analyzer section 252 c, areas follows. The data map contents can be appropriately corrected basedon results that are obtained during operation of the electric powerconverter apparatus 2. The map data can thereby be amended to beaccurately in accordance with the actual operating characteristics ofthe electric power converter apparatus 2. It can thereby be reliablyensured that the amplitude of specific high-frequency (harmonic)components of the ripple current in the output current from the electricpower converter apparatus 2 will be effectively reduced.

The invention is not limited to the configuration for the secondembodiment described above, and it would be equally possible for theelectric power converter apparatus to be formed of three or moreelectric power converter circuits with a corresponding set of three ormore control circuits.

In that case, each of the control circuits includes a PWM signalgenerating circuit, one of the control circuits includes a circuit forgenerating a signal used as a phase reference for PWM signal generation,each of the other control circuits includes a phase difference settingcircuit and a stored data map which relates values of PWM signal phasedifference to corresponding values of PWM duty ratio, and at least oneof the control circuits includes a data map correction section.

Third Embodiment

A third embodiment is described in the following. The electric powerconverter apparatus 3 of this embodiment utilizes a pair of data maps,respectively corresponding to AM-band and FM-band frequency ranges asdescribed in the following, but is otherwise similar to the secondembodiment described above.

The configuration of the third embodiment will first be describedreferring to FIGS. 11 and 12. Only the features of difference from thesecond embodiment will be described in detail. As shown in FIG. 11, theelectric power converter apparatus 3 of the third embodimentincorporates a control circuit 35, which includes an oscillator circuit350, a PWM control value setting circuit 351 and a PWM signal generatingcircuit 353 that are respectively identical to the oscillator circuit250, the PWM control value setting circuit 251 and the PWM signalgenerating circuit 253 in the control circuit 25 of the secondembodiment. The control circuit 35 further includes a phase differencesetting circuit 352, whose function and operation are identical to thoseof the phase difference setting circuit 252 of the second embodiment,other than with respect to use of the AM-band, FM-band data maps, whichare held stored in the phase difference setting circuit 352.

As shown in FIG. 12, the phase difference setting circuit 352 is formedof a data map storage section 352 a, a phase difference setting section352 b, a frequency component analyzer section 352 c, a data mapcorrection section 352 d, a target amplitude value storage section 352e, and a frequency component designation section 352 f. The function ofthe data map correction section 352 d is identical to that of the datamap correction section 252 d of the second embodiment described above.The frequency component analyzer section 352 c has a similar function tothat of the frequency component analyzer section 252 c of the secondembodiment, but is required to execute frequency analysis over a rangewhich includes both the AM-band and FM-band radio frequency ranges. TheFM-band frequency range of a vehicle-installed radio receiver isgenerally 76 MHz˜90 MHz.

The AM-band data map that is stored in the data map storage section 352a is identical to the AM-band data map in the data map storage section252 a of the second embodiment, i.e., in which each of respective valuesof PWM signal duty ratio is linked to a corresponding value of phasedifference between the PWM signals from the control circuit 34 andcontrol circuit 35 whereby the amplitude of frequency components (ripplecurrent harmonic frequency components) in the output current from theelectric power converter apparatus 3, within the AM-band frequencyrange, is minimized. The FM-band data map that is stored in the data mapstorage section 352 a similarly links each of the duty ratio values to acorresponding stored value of PWM signal phase difference. However inthis case, the corresponding value of phase difference is predeterminedsuch as to minimize the amplitude of ripple current frequency componentsthat are within the FM-band frequency range (76 MHz˜90 MHz).

The functions of the target amplitude value storage section 352 e andfrequency component designation section 352 f are as follows. The targetamplitude value storage section 352 e stores a target value of frequencycomponent amplitude. The 352 f receives the frequency analysis resultsobtained by the frequency component analyzer section 352 c, i.e.,respective amplitude values of frequency components that are within theAM-band and FM-band frequency ranges. The frequency componentdesignation section 352 f compares these respective amplitude valueswith the target value that is held in the target amplitude value storagesection 352 e. If any of these amplitude values is judged to exceed thetarget value, the frequency component designation section 352 fdetermines the frequency component (referred to in the following as thedesignated frequency component) whose amplitude exceeds the target valueby the greatest extent. The designated frequency component is identifiedas being a frequency component whose amplitude is required to bereduced. Specifically, the frequency component designation section 352 finputs a signal to the phase difference setting section 352 b indicatingthe judgement result, i.e., indicating whether the designated frequencycomponent is within the AM-band or within the FM-band frequency range.

In that way, when the duty ratio that is set by the PWM control valuesetting circuit 351 becomes changed, and it is then determined by thefrequency component designation section 352 f that one or more of theripple current frequency components has excessively high amplitude, theappropriate one of the AM-band and FM-band data maps is selected by thephase difference setting section 325 b in accordance with thedesignation result from the frequency component designation section 352f. The value of PWM phase difference corresponding to the newly setvalue of duty ratio is then read out from the selected data map, and thephase difference between the PWM signals from the control circuits 34and 35 respectively is set accordingly.

In that way the most suitable one of the AM-band and FM-band data mapsis selected, for appropriately reducing the amplitude of the ripplecurrent frequency components.

In other respects, the operation and configuration of the thirdembodiment are identical to those of the second embodiment describedabove.

The third embodiment has been described above for the case of utilizingtwo data maps, respectively corresponding to the AM-band and FM-band ofradio frequencies. However it would be equally possible to utilize threeor more of such data maps, corresponding to respectively different radiocommunication frequency ranges. This is illustrated in FIG. 13, in whichthe data map storage section 352 a of the phase difference settingcircuit 352 stores a total of n data maps, corresponding to respectivefrequency ranges f1, f2, . . . fn.

The invention has been described above referring to specificembodiments, however the invention is not limited to these, and variousalternative forms or modifications of the embodiment or combinations offeatures from respective embodiments may be envisaged, which fall withinthe scope of the invention as set out in the appended claims.

What is claimed is:
 1. An electric power converter apparatus comprisinga plurality of electric power converter circuits having respective pairsof input terminals connected in parallel and respective pairs of inputterminals connected in parallel, each of the electric power convertercircuits comprising a plurality of switching elements and beingcontrolled by a corresponding PWM (pulse width modulation) controlsignal for executing switching of the switching elements, for convertinginput electric power supplied to the input terminals to output electricpower produced from the output terminals; and control circuitryconfigured to generate a plurality of PWM signals mutually differing inphase by a specific phase difference and each being of identicalfrequency, and to supply the PWM signals as the corresponding PWMcontrol signals to respective ones of the electric power convertercircuits; wherein the control circuit is configured to set the specificphase difference at a value for minimizing an amplitude of specificripple current frequency components of a ripple current, the ripplecurrent being present in a combined output current comprising acombination of respective output currents produced from the plurality ofelectric power converter circuits.
 2. The electric power converterapparatus according to claim 1, wherein the plurality of PWM signalshave an identical value of PWM duty ratio, and wherein the controlcircuitry comprises: a data map relating each of respective values ofthe PWM duty ratio to a corresponding value of phase difference, thecorresponding value of phase difference being predetermined forminimizing an amplitude of the ripple current frequency components whenthe corresponding value of PWM duty ratio is set; and, a phasedifference setting section configured for obtaining, from the data map,a phase difference value corresponding to a value of PWM duty ratio thatis currently set, and for setting the obtained phase difference value asthe specific phase difference.
 3. The electric power converter apparatusaccording to claim 2, wherein the control circuitry comprises: afrequency component analyzer section configured to derive analysisresults expressing respective amplitude values of the ripple currentfrequency components; and a data map correction section configured tocorrect each of respective ones of the phase difference values stored inthe data map, based on analysis results derived by the frequencycomponent analyzer section when the PWM duty ratio corresponding to thephase difference value has become set by the control circuitry.
 4. Theelectric power converter apparatus according to claim 1, wherein theplurality of PWM signals have an identical value of PWM duty ratio andthe control circuitry is configured to selectively set the value of thePWM duty ratio, and wherein the control circuitry comprises: a frequencycomponent analyzer section configured to derive analysis resultsexpressing respective amplitudes of the ripple current frequencycomponents; a plurality of data maps corresponding to respectivelydifferent frequency ranges, each data map relating each of respectivevalues of the PWM duty ratio to a corresponding value of the specificphase difference, the corresponding value being predetermined forreducing a highest amplitude of specific ripple current frequencycomponents to a minimum amplitude value, the specific ripple currentfrequency components being within the frequency range corresponding tothe data map; and a frequency component designation section configuredto specify one of the ripple current frequency components as adesignated frequency component; wherein the phase difference settingsection is configured to select a data map that corresponds to afrequency range containing the frequency of the designated frequencycomponent, and to obtain the value for the specific phase differencefrom the selected data map.
 5. The electric power converter apparatusaccording to claim 4, wherein: the control circuitry comprises afrequency component analyzer section configured to derive analysisresults expressing respective amplitude values of the ripple currentfrequency components; and the frequency component designation section isconfigured to specify the designated frequency component based upon theanalysis results from the frequency component analyzer section.
 6. Theelectric power converter apparatus according to claim 5, wherein: thecontrol circuitry comprises a target value memory section having storedtherein a target value of frequency component amplitude, and thefrequency component designation section is configured to specify thedesignated frequency component as a ripple current frequency componenthaving an amplitude that exceeds the target value of frequency componentamplitude by a greater amount than any other of the ripple currentfrequency components.
 7. The electric power converter apparatusaccording to claim 5, wherein the control circuitry comprises a data mapcorrection section configured to correct each of respective ones of thephase difference values stored in the data map, based on analysisresults derived by the frequency component analyzer section while theduty ratio corresponding to the phase difference value is set by thecontrol circuitry.
 8. The electric power converter apparatus accordingto claim 2, wherein the data constituting the data map are derived basedupon results of computer simulation.
 9. The electric power converterapparatus according to claim 1, wherein the plurality of electric powerconverter circuits and the control circuit are respectively installed ina vehicle.
 10. The electric power converter apparatus according to claim1, wherein the control circuitry comprises a plurality of controlcircuits generating respective ones of the plurality of PWM signals,wherein a frequency of a PWM signal generated by one of the controlcircuits is utilized as a reference frequency by each of remaining onesof the control circuits in generating remaining ones of the plurality ofPWM signals.